The invention relates to image and video display. More specifically, the invention relates to methods and apparatus for discouraging the unauthorized copying of digital color images and video sequences.
Digital Versatile Disc (DVD) players are providing consumers with access to wide screen movies having high quality images and high fidelity sound. The high quality format of the DVD players brings theatre-like entertainment to the home.
However, the high quality format of DVD players also allows high quality copies to be made on videocassette recorders. Anyone with a videocassette recorder has the ability to make professional quality VHS copies of their DVD releases. In the absence of a copy protection scheme, quality of the unauthorized VHS copies is generally comparable to the quality of VHS originals sold in stores. Therefore, unauthorized copying and distribution of DVD releases poses a challenge for copyrights owners who want to protect their intellectual property rights and store owners who want to protect their videocassette businesses.
The DVD players presently utilize a copy protection scheme that is transparent to the images being displayed by the DVD player. Trigger bits are set on a DVD disc. While the DVD disc is being played, the trigger bits activate a certain digital-analog converter chip inside the DVD player. The chip then applies copy protection to an NTSC output of the DVD player.
This copy protection scheme is based on differences in the way VCRs and televisions operate. The automatic gain control (AGC) circuits within a television are designed to respond slowly to change, whereas the AGC circuits within a VCR are designed to respond quickly to change. The scheme attempts to take advantage of these differences by modifying the video signal so that quality of the original video signal will be unaffected when displayed on a television, yet quality of an unauthorized copy of the video signal will be degraded. When the NTSC output of the DVD player is recorded on a VCR, the resulting VHS copies will typically have reduced viewability or quality.
However, attempts are being made to defeat the copy protection scheme utilized by the DVD players. Commercial "stabilizers" are presently available on the market.
Moreover, the copy protection scheme can be defeated on DVD-ROM drives for computers. A DVD-ROM drive allows the same high quality format videos to be played on a computer monitor. However, the DVD-ROM drive does not output an NTSC signal. Instead it outputs an analog RGB signal, which is unprotected between the computer and the monitor. An RGB-NTSC converter between the computer and the monitor can convert the unprotected RGB signal to the NTSC domain for storage on a videocassette or other recorder. Thus, a simple RGB-to-NTSC converter would allow a person to bypass the copy protection scheme on the DVD-ROM drive and record the video on a videocassette recorder.
Home copying and professional piracy remain great threats to artists, producers, copyrights owners and owners of videocassette businesses. There is still a need for discouraging the unauthorized copying and distribution of images and video sequences, especially with regards to DVD-ROM drives for computers.